Voltage regulator with zero current static switching between tapped portions of the primary of a regulator transformer

ABSTRACT

The secondary winding of a transformer is series connected between a source of unregulated voltage and a load. Gated bilateral semiconductor switches are selectively triggered to connect segments of the primary winding of the transformer across the unregulated voltage source such that incremental voltages having either bucking or boosting polarities appear across the secondary winding. A further gated bilateral semiconductor switch is provided for shorting each segment should neither bucking nor boosting voltage be required.

United States Patent Clarence J. Kettler Lenox, Mass.

Apr. 16, 1970 Nov. 16, 1971 General Electric Company Inventor Appl. No. Filed Patented Assignee VOLTAGE REGULATOR WITH ZERO CURRENT STATIC SWITCHING BETWEEN TAPPED PORTIONS OF THE PRIMARY OF A REGULATOR TRANSFORMER 8 Claims, 4 Drawing Figs.

US. Cl 323/435 S, 323/45, 323/62 Int. Cl 605i 1/30 Field otSearch 323/6, 24,

[56] References (11160 UNITED STATES PATENTS 1,914,193 6/1933 Bedford 323/43.5s 1,959,153 5/1934 Blume 323/45 3,l29,380 4/1964 Lichowsky 323/45 3,28l,652 10/1966 Perrins 323/43.5s 3,388,319 6 1968 Paynter.. 323/43.5s 3,419,788 12/1968 May 323/6 3,530,369 9/1970 Thompson 323/4358 Primary Examiner-A. D. Pellinen Attorneys-Doyle, Francis X., Vale P. Myles, Frank L.

Neuhauser, Oscar B. Waddell and Joseph B. F onnan ABSTRACT: The secondary winding of a transformer is series connected between a source of unregulated voltage and a load. Gated bilateral semiconductor switches are selectively triggered to connect segments of the primary winding of the transformer across the unregulated voltage source such that incremental voltages having either bucking or boosting polarities appear across the secondary winding. A further gated bilateral semiconductor switch is provided for shorting each segment should neither bucking nor boosting voltage be required.

1 ZERO CURPf/Vr DEIZOTOR TR/GGfR CONTROL {5) B/lATER/M 72/065950 SEMICONDUCTOR Sly/7'67! BACKGROUND OF THE INVENTION This invention relates generally to voltage magnitude control systems and, more particularly, to such systems which utilize selectively controlled semiconductor devices for providing a regulated voltage to a load.

The ever increasing need for providingaccurate, predictable voltage levels in the fields of chemical processing, industrial instrumentation, and other areas has resulted in more exacting requirements for voltage regulation systems. Voltage regulation systems are required which respond rapidly and accurately, and can regulate load voltage within small tolerances. In the past, line voltages have often been regulated by means of mechanical contactors and tap selectors which mechanically make and break a circuit in order to select that tap of a supply transformer which provides the desired line voltage. Because such systems have been subject to arcing, mechanical wear and degradation, and have been relatively slow, newer types of switching and regulating arrangements have been devised. In one such anarrangement segments of a secondary winding of a supply transformer may be selectively connected in series with a load, or bypassed, by bilateral switches comprising pairs of inverse parallel connected SCR's which are gated bya control unit. See U.S. Pat. No. 3,195,038. However, with this arrangement, if a given segment of the secondary winding is connected in a circuit the switch in series therewith is alsoin the circuit; and if, on the other hand, the winding segment is to be bypassed the bypass or shunting switch must then be in the circuit instead. Whilesuch an arrangement may be acceptable under high-voltage conditions, the forward voltage drop across the semiconductor switches becomes a significant portion of the available voltage for low voltage, e.g., 1 l and 220 volt, applications. Copending application Ser. No. 29,082 for Static Voltage Regulator Circuit, by the present inventor, and assigned to the present assignee, teaches circuits making use of such semiconductor switches which do not incorporate such switches in series with a load circuit, but utilize them for placing the primary windings of regulating transformers across preselected portions of an output winding of a supply transformer.

SUMMARY OF THEINVENTION The present invention contemplates the connection of the secondary windings of one or more transformers in series between a source of unregulated voltage and a load. Gated, bilateral semiconductor switches are provided to selectively connect the primary winding to a source of unregulated voltage so as to induce either an additive or boosting," or a subtractive or bucking," voltage increment in the secondary winding. A first side of another such switch is coupled to the center tap of the primary winding, the second side of such switch being coupled to both ends of the primary winding by means of two additional switches. In this manner, one half of the primary winding may alone be energized to provide a boosting voltage which is twice the boost obtained from the use of the entire primary winding, or the other half of the winding may be connected with reversed polarity to provide a bucking voltage which is twice that which is afforded by the reversal of the entire primary winding.

It is therefore an object of the present invention to provide a voltage regulation circuit utilizing gated bilateral semiconductor switches without introducing such switches into the load circuit.

It is a further object of the present invention to provide an in-line regulating transformer having various output voltages without the necessity of applying different voltages to be primary winding thereof.

The invention sought to be protected will be clearly pointed out and distinctly' claimed in the claims appended hereto. However, it is believed that this invention and the manner in which its various objects and advantages are obtained will be better understood by reference to the following detailed descriptions of preferred embodiments, especially in the light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a voltage regulation transformer generally indicated at 10 has its secondary winding 12 connected in series between'a source or unregulated voltage V and a load 14. The primary winding 16 of the regulating transfonner is provided with a center tap which divides the winding into first and second segments P, and P, Gated, bilateral semiconductor switches S, and 8,, which are normally nonconducting, connect the ends of primary winding to one terminal of voltage source V while switches S, and S, connect the winding ends to a common, or ground, potential constituting the other terminal of the voltage source V A further switch S, couples the center tap to common or ground potential.

In order to teach the invention more clearly, one end of the primary and secondary windings is marked with a denominating what will hereinafter be described as the positive end of the winding. With the polarities indicated at FIG. 1, it will be apparent that connection of the marked end of primary winding 16 to the nongrounded side of voltage source V and the center-tapped or the unmarked end to ground, results in the presence of an additive voltage increment V across the terminals of secondary winding 12. More particularly, it will be seen that switch S, connects first, positive" end of winding 16 to one side of voltage source V Similarly, switch S, connects the opposite or second, negative," end of the primary winding to the same one side V Switches S, and S, connect the positive and negative ends, respectively, of primary winding 16 to a point ofground potential comprising the other side of V The switches are operated by a control mechanism generally indicated at 18. Control 18 is advantageously constrained to selectively operate switches S through 8,, upon reception of a signal from zero-current detectors 30 and 32, as will be described hereinafter.

The control mechanism includes a plurality of trigger elements S, through S, each of which is coupled to a switch having a corresponding designation. When, for example, trigger element S, is actuated it produces a pulse which is transmitted to switch S lenergizing the switch. Similarly, trigger elements S, through S, may be selectively actuated to energize preselected ones of switches S, through 8,.

It will be understood by those skilled in the art that the voltage increment V, which appears across the secondary winding 12 of regulating transformer 10 is related to the voltage appearing across primary winding 16 in the ratio of the turns of secondary to the turns of the primary windings. It will also be understood that by energizing only one half of primary wind ing 16, the number of effective turns of primary 16 will be reduced by one half, so that the voltage regulating increment V would then be twice the increment V, which occurs when the full winding 16 is energized by V Similarly, if primary winding 16 is reversed across voltage source V the polarity of the regulating voltage V,, appearing across the secondary winding 12 will also reverse.

For purpose of illustration, it will now be assumed that when V,- is applied to the positive" end of primary winding I6, and

only the negative" end of the primary winding is connected to ground, a 1 percent additive or boosting" voltage V,, will appear across secondary winding 12, thus increasing the voltage supplied to load 14 by 1 percent.

FIG. 2 shows, in tabular form, the percentage regulating voltage V, which appears across secondary winding 12 of transformer 10 when selected ones of switches S, through S,, are energized, such energization being indicated by the presence of an X in the column designating the switch. Should a full 2 percent boosting V designated as +2," be desired, it will be seen that such an additive voltage is obtained by energizing switches S, and S, which places one half of primary winding 16, designated as P,, across unregulated supply voltage boost, or a 1 percent boost, may be obtained by energizing switches S, and S, and deenergizing switch S to place voltage V across the full length of primary winding 16. Conversely a subtractive or bucking" voltage V appears across secondary winding 12 when primary winding 16 is connected in a reverse manner across V Should switches S, and S, be energized, it will be seen that the negative" end of the primary winding will be coupled to the source of voltage to which the positive end has previously been coupled to provide a boosting voltage V With the full length of primary winding 16 thus energized, a bucking voltage of 1 percent will be provided. Should twice as large a bucking voltage V,, be desired, S is deenergized and S and S, energized to place winding segment P across unregulated voltage V The turns ratio of transfonner 10 is thus halved, and bucking voltage V,, doubles. in the event that neither a bucking nor a boosting voltage is desired, switches S and S, may be energized to short circuit he entire primary winding 16.

It will thus be seen that by using a single transfonner associated with five bilateral switches S, through 8,, a total of five regulating voltage increments can be obtained. The switch voltage drops, however, are negligible when referred to the load circuit thus rendering the device well suited for low-voltage use. Still further, due to the speed with which semiconductor switches S, through S, may be operated, zero current detectors 30 and 32 may be employed to constrain control unit 18 to operate switches S, through S, only at the zero current, or crossover point, of the system current. A minimal disturbance of line current thus occurs with few undesirable harmonics being produced thereby.

Referring now to FIG. 3, a multiple stage regulating apparatus is shown. A first stage comprising a transformer generally indicated at 10 is provided, which may take the form of the circuit shown in FIG. 1. A second transformer generally indicated at 20 is also provided, the secondary winding 22 thereof being connected in series with the secondary winding 12 of transformer 10 and load 14. Gated bilateral semiconductor switches 8,, --S,,, are provided to selectively energize the primary winding 16 of regulating transformer 10, as previously described. Corresponding switches 8,, -8 are coupled to points on primary winding 26 of second regulating transformer 20 in a similar manner. It will be noted, however, that the primary windings of both regulating transformers l and 20 derive their voltages from unregulated supply voltage V Control 18 is provided to selectively trigger semiconductor switches S,, -S,,, in the proper combinations to provide desired incremental voltages V,, at secondary winding 12. Control unit 28 performs a similar function for switches 8,, -8 of the second stage, resulting in the production of a second incremental voltage V',,. Zero current detectors 30, 32 supply signals to both controls 18 and 28 so that the controls may trigger their associated switches at zero current, thus eliminating unwanted harmonic disturbances in the load current waveform.

Since regulating transformers and 20 are in series, deriving their primary voltage from a common source, it will be apparent that the incremental change in voltage experienced by load 14 is the algebraic sum of the two voltage increments V,, and V, supplied by transformers l0 and 20, respectively. While values of the incremental voltages provided by the transformers may be of any magnitude desired, for purposes of illustration it will be assumed that the turns ratio of the windings l2 and 16 of regulating transformer 10 is such that V,, may be 0, =1, or =2 percent of supply voltage and the turns ratio of the windings 22 and 26 of second stage regulating transformer 20 is such as to provide voltage increments of 0, =5, or =l0 percent. It will now be apparent to those skilled in the art that the increments thus supplied may be selectively combined to provide voltage regulation over a range of from 1 2 percent to +12 percent in incremental steps of l percent each.

FIG. 4 is a schematic diagram showing a gated, bilateral semiconductor switch generally indicated as S and of a type usable with the inventive circuits. A pair of SCRs 40 and 42 are coupled in inverse parallel a relationship so that the SCRs conduct current in opposite directions. SCRs 40 and 42 are triggered on alternate half cycles of system current by trigger element 8' of control 18 which is constrained to operate when line current is zero, that is, at the crossover point" of the AC waveform. A pair of diodes 31, 33 are connected in inverse parallel relationship and placed in series with primary winding 16 of a regulating transformer 10. Since this current path is not always active, a second pair of diodes 38 and 39, also connected in parallel relationship, are placed in series with either of the other two current carrying connections of primary winding 16. As the polarity of current in the primary winging reverses, the voltage drop across one or both diode pairs also reverses initiating a pulse in the primary windings of isolation transformers 34 or 37, or both, which is transmitted through full wave rectifiers 35 or 36 to control 18.

Although the present invention has been described with reference to particular circuit, various modifications may be made by those skilled in the art without departing from the spirit and scope of the invention. It will be recognized, for instance, that various types of bilateral semiconductor switches may be utilized. Further, dissimilar stages of regulating transformers may be provided such that some stages provide a grater number of bucking or boosting voltage increments than others. The various circuits described herein are merely exemplary and modifications may be made thereof departing from the system as described and claimed herein. Therefore, the appended claims are intended to cover all such equivalent variations which come within the true spirit and scope of the inventron.

What is claimed as new and is desired to be secured by Letters Patent of the United States is:

l. A voltage-regulating system comprising:

a regulating transformer including a secondary winding adapted to be connected between a source of unregulated voltage and a load, and a primary winding having a first and a second end, and having at least one tap intermediate said ends;

first and second gated bilateral semiconductor switches for connecting said first and said second end of said primary winding to a first side of a source of unregulated voltage;

third and fourth gated bilateral semiconductor switches for connecting said first and said second end of said primary winding to a second side of the source of unregulated voltage;

fifth gated bilateral semiconductor switch means for selectively connecting said at least one tap intermediate the ends of said primary winding to said second side of said source of unregulated voltage; and

control means for selectively energizing said switches.

2. A voltage regulating system as defined in claim 1 wherein said primary winding is provided with a single tap intermediate said first and said second ends of said primary winding, said tap dividing said primary winding into two segments having equal numbers of turns.

3. A voltage-regulating system as defined in claim 1, further including means responsive to the crossover point of current in said primary winding for causing said control device to selectively trigger said gated bilateral semiconductor switches at said crossover point.

4. A voltage-regulating system as defined in claim 1 wherein said gated bilateral semiconductor switches comprise pairs of SCRs connected in inverse parallel relationship.

5. A voltage-regulating system comprising:

a first regulating transformer including a secondary winding 5 source;

gated bilateral semiconductor switching means for selectively coupling said first or said second ends of said primary windings of said first or said second transformer to a second side of said source of unregulated voltage;

adapted to be connected in series between a load and a first side of a source of unregulated voltage, and having a primary winding having a first and a second end, said primary winding being divided into a pair of segments by a gated bilateral semiconductor switching means for coupling said tap intermediate the ends of said primary windings to said second side of said voltage source; and

control means for selectively energizing said switches.

6. A voltage-regulating system as defined in claim 5 wherein said taps intermediate said first and said second ends of said primary windings divide said primary windings into segments having equal number of turns.

7. A voltage-regulating system as defined in claim 5 further including means responsive to the crossover point of current in one of said primary windings for causing said control means to selectively trigger said switches at said crossover point.

8. A voltage-regulating system as defined in claim 5 wherein tively coupling said first or said second ends of said isaid gated bilateral semiconductor switches comprise pairs of mary windings of said first or said second regulating trans- 2O SCR 5 connected m mverse Parallel relauonshlp former to said first side of said unregulated voltage tap intermediate said ends; a second regulating transformer having a secondary winding adapted to be connected in series with said secondary winding of said first regulating transformer between said load and said first side of said source of unregulated voltage, and having a primary winding having a first and a second end, said pril5 mary winding being divided into a pair of segments by a tap intermediate said ends;

gated bilateral semiconductor switching means for selec- CERT?EECA'EEQ (9i IQ (l'iEQN Patent NO. 3,621. 375 Dated November 16, 1971 Inventor) olarence a Kettler It is certified that error appears in the above-identified patent and that said Letters Patent are hereby cqrrected as shown below:

Col. 2, line +5, after "side" insert of line 69, "V should be V Col. Q line 13, after voltage" insert V Similarly one half of this voltage line 31, "129. should be the Col. 4-, line 4, :1, or :2 should be +1, or +2 line 7 :5 or =10 should be +5, or +10 line 28, "winging should be winding line 39, "grater should be greater 

1. A voltage-regulating system comprising: a regulating transformer including a secondary winding adapted to be connected between a source of unregulated voltage and a load, and a primary winding having a first and a second end, and having at least one tap intermediate said ends; first and second gated bilateral semiconductor switches for connecting said first and said second end of said primary winding to a first side of a source of unregulated voltage; third and fourth gated bilateral semiconductor switches for connecting said first and said second end of said primary winding to a second side of the source of unregulated voltage; fifth gated bilateral semiconductor switch means for selectively connecting said at least one tap intermediate the ends of said primary winding to said second side of said source of unregulated voltage; and control means for selectively energizing said switches.
 2. A voltage regulating system as defined in claim 1 wherein said primary winding is provided with a single tap intermediate said first and said second ends of said primary winding, said tap dividing said primary winding into two segments having equal numbers of turns.
 3. A voltage-regulating system as defined in claim 1, further including means responsive to the crossover point of current in said primary winding for causing said control device to selectively trigger said gated bilateral semiconductor switches at said crossover point.
 4. A voltage-regulating system as defined in claim 1 wherein said gated bilateral semiconductor switches comprise pairs of SCR''s connected in inverse parallel relationship.
 5. A voltage-regulating system comprising: a first regulating transformer including a secondary winding adapted to be connected in series between a load and a first side of a source of unregulated voltage, and having a primary winding having a first and a second end, said primary winding being divided into a pair of segments by a tap intermediate said ends; a second regulating transformer having a secondary winding adapted to be connected in series with said secondary winding of said first regulating transformer between said load and said first side of said source of unregulated voltage, and having a primary winding having a first and a second end, said primary winding being divided into a pair of segments by a tap intermediate said ends; gated bilateral semiconductor switching means for selectively coupling said first or said second ends of said primary windings of said first or said second regulating transformer to said first side of said unregulated voltage source; gated bilateral semiconductor switching means for selectively coupling said first or said second ends of said primary windings of said first or said second transformer to a second side Of said source of unregulated voltage; gated bilateral semiconductor switching means for coupling said tap intermediate the ends of said primary windings to said second side of said voltage source; and control means for selectively energizing said switches.
 6. A voltage-regulating system as defined in claim 5 wherein said taps intermediate said first and said second ends of said primary windings divide said primary windings into segments having equal number of turns.
 7. A voltage-regulating system as defined in claim 5 further including means responsive to the crossover point of current in one of said primary windings for causing said control means to selectively trigger said switches at said crossover point.
 8. A voltage-regulating system as defined in claim 5 wherein said gated bilateral semiconductor switches comprise pairs of SCR''s connected in inverse parallel relationship. 